Hardening agents for gelatin coating compositions



United States Patent 3,505,071 HARDENING AGENTS FOR GELATIN COATINGCOMPOSITIONS Salvatore Emmi, Binghamton, N.Y., assignor to GAFCorporation, New York, N.Y., a corporation of Delaware No Drawing. FiledMar. 14, 1967, Ser. No. 622,921 Int. Cl. G03c 1/30 US. Cl. 96-111 6Claims ABSTRACT OF THE DISCLOSURE Hardening agents for gelatin coatingcompositions comprising butyne and propene derivatives.

The present invention relates in general to the hardening of gelatin andin particular to the hardening of photographic gelatin and gelatinosilver halide emulsions whereby to yield compositions having anappreciable increase in melting point as well as good stability on agingwith respect to fog, speed, tonal gradation and the like.

In the preparation of photographic gelatin dispersions and gelatinosilver halide emulsions, it has been customary practice to treat thedispersion or emulsion at some stage prior to actual coating on a filmbase with a hardening agent, i.e., a substance capable of reducing thetendency of the gelatin to soften, distend or otherwise dissipatestructurally due to environmental influences, e.g., as a result ofsubjection to photographic processing solutions. The incorporation ofhardening agents into gelatinbased coating compositions is for the mostpart deemed vital in order to provide a final laminate element possessedof the requisite structural stability. As will be recognized, manycommercial operations such as those associated with high speedphotoreproduction may in some instances dictate the use of processingtemperatures considerably in excess of those specified as efficaciousfor the particular photographic material in question having due regardto the nature of the emulsion addenda. The published literature, bothpatent and otherwise, is of course replete with reference to hardeningmaterials which may be employed for the aforedescribed purposes withparticular representatives including, for example, formaldehyde,hydroxyaldehydes, acrolein, glyoxal and derivatives thereof and mixturesof an aliphatic aldehyde with an aromatic compound containing at leastone nuclearly substituted hydroxy group such as phenol, resorcinol,resorcylic aldehyde and the like. Although many of the hardening agentsof the foregoing type have provided to be somewhat effective as regardsimparting the desired hardening effects to the gelatin medium containingsame, their use is invariably attended by one or more disadvantages. Forexample, and with particular reference to the problems attending theprovision of gelatin-silver halide emulsions having optimum viscositycharacteristics, it is often found that the hardening agent in questionexhibits a pronounced tendency to deleteriously affect the sensitometriccharacteristics of the product emulsion leading to the formation ofexcessive fog, desensitization as well as a general flattening ofgradation in the image obtained. In general, those hardening agentswhich can be categorized as formaldehyde liberators are found, almostinvariably to be possessed of the aforedescribed objectionable featuresas well as that of after hardening.

The foregoing situation has stimulated considerable industrial activitycentered around the research and development of substances, which, whiledevoid of any tendency to affect adversely the sensitometriccharacteristics of the gelatin emulsion would nevertheless provideoptimum hardening effects. Despite the meritorious achievement in thisregard, the overall improvement has proved 3,505,071 Patented Apr. 7,1970 to be marginal. For example, many of the hardening agents proposedand which purportedly minimize the aforedescribed deleterious effectsare capable of exerting hardening effects only when subjected toelevated temperatures. Unfortunately, the accompanying thermal effectsare in many instances destructive of the photographic properties of theemulsion material and especially those of the high speed type.

In certain photographic applications it is of critical importance thateach of the gelatin layers present in the photographic element, whetherlight sensitive or not, be resistant to water at elevated temperatures.This would be the case, for example, with high speed reproductionwherein processing solutions, e.g., developer, fixer, etc. are of anespecially high order of activity. For the most part, those hardeningagents considered to be more or less conventional have provedintolerably deficient for use with emulsions contemplated for high speedprocessing. In addition, it has been observed that many of the hardeningagents specifically devised for high speed processing cause incubationfog and/ or undesired after hardening, i.e., continued hardening of thegelatin during storage. As will be readily apparent, such properties arehighly objectionable and may well result in development restraint.Moreover, with photographic silver halide emulsions intended for use inthe formation of colored images and wherein color coupling compounds areemployed for such purposes, inter-reaction of the hardening agent withthe color coupling components may be encountered.

It is thus manifestly clear that the advent of high speed processtechniques has imposed additional and stringent requirements on thenature of the hardening agent which may be effectively employed.Firstly, it is imperative that the hardening agent be of the delayedaction type, i.e., the hardening result does not obtain until actualprocessing of the photographic emulsion. Any premature hardening actionwill, as a practical matter, make emulsion handling extremely difficultif not impossible. This Will be readily appreciated since the viscosityincrease effected in the gelatin medium tends to vitiate any possibilityof obtaining a uniform coating of the desired thickness. Secondly, andin view of the rather severe processing conditions characterizing highspeed processing, it is absolutely imperative that the hardening agentbe capable of exerting significant hardening effects whereby to renderthe gelatin layer containing same structurally stable and thusimpervious to the effects of such conditions. Any defect in structuralintegrity will of course be aggravated by the use of processingconditions involving severe temperatures, solution activity, etc. and inall likelihood render the element unsuitable for commercial use.

Thus, the primary object of the present invention resides in theprovision of hardening agents for incorporation into gelatin coatingcompositions wherein the foregoing and related disadvantages areeliminated or at least mitigated to a substantial extent.

Another object of the present invention resides in the provision ofhardening agents for photographic silver halide emulsions, said agentsproviding a delayed hardening action, i.e., the viscosity-increasingeffects imparted by such compounds are not evident until processing ofthe exposed emulsion.

A further object of the present invention resides in the provision ofhardening agents beneficially adapted for use with gelatin silver halideemulsions, said agents being totally devoid of any tendency todeleteriously affect the emulsion properties such as fog, speed,contrast, density and the like.

Other objects and advantages of the present invention will becomeapparent hereinafter as the description proceeds.

The attainment of the foregoing and related objects is made possible inaccordance with the present invention which in its broader aspectsincludes the provision of delay action hardening agents comprising atleast one compound selected from the group consisting of those of thefollowing structural formulae:

wherein X represents hydroxy or halogen, e.g., chloro, bromo, etc. and Yrepresents halogen, e.g., chloro, bromo, etc.

As specific examples of compounds falling within the ambit of the abovestructural formulae there may be mentioned the following:

1,4-butynediol 1,4-dichlorobutyne 3-bromopropene Methods for thepreparation of such compounds are extensively described in theliterature both patent and otherwise. Moreover, such compounds arereadily available commercially, e.g., from the GAP Corporation.

The hardening agents encompassed by the above formula may beadvantageously employed in any of the layers normally associated whollyor partly of gelatin, whether such layer be light-sensitive or not. Aswill be appreciated, the urgency surrounding the obtention ofsatisfactory structural stability exists with regard tonon-light-sensitized layers as well. Thus, the hardening agentsdescribed herein may be incorporated into any of the auxiliary layerscontaining significant quantities of gelatin, e.g., anti-halation layer,anti-abrasion or anti-static layer, and/or subbing layer. The latterembodiment is found to provide a significant measure of improvement inoverall structural stability since, the presence of the hardening agenttends to augment considerably the primary function of the subbing layer,namely, the promotion of a firm adhesive bond between the support andsubsequently applied layers.

The hardening agents described above may be added to the gelatinsolution and/or light-sensitive silver halide emulsion at any convenientstage of the preparation. For example, such agents may be added shortlyprior to coating the gelatin medium onto a suitable support, which maybe glass, paper, cellulose, cellulose derivatives, or other suitablematerial conventionally employed for such purposes in the preparation ofphotographic elements.

Alternatively, such hardening agents may be incorporated subsequent tocoating the gelatin medium onto the base material, e.g., by immersingthe fabricated film element in a solution of the hardener. Theattainment of optimum characteristics quite obviously will depend uponthe selection of conditions of temperature, time of immersion,concentration and pH, these values being capable of ready determinationin a particular instance.

The hardening agent can be conveniently provided in the form of asuitable solution in a water miscible solvent, e.g., methanol, ethanol,acetone, etc. as well as mixtures of one or more in water inconcentrations ranging from about 1% to about 20%. The concentration ofthe hardener solution is not particularly critical per se and isselected solely for purposes of affording maximum control when added tothe emulsion, film element, etc.

The amount of hardening agent actually incorporated into the gelatincoating composition will depend primarily on the desired increase inmelting point. Thus, it has been found that substantial increases inmelting point of photographic materials may be obtained by addingamounts sufiicient to yield a hardener concentration within the range offrom about .005 part to about 0.20 part per part of dry gelatin. Again,the foregoing concentration limitations are significant solely from thestandpoint of assuring maximum realization of optimum hardening effects.It

EXAMPLE I This example illustrates the improvement obtained in meltingpoint characteristics in a simple gelatin coating composition, i.e., ofthe type which would be suitable for use as an auxiliary layer in thefabrication of photographic film elements. As will be noted from theinspection of Table I below, melting point evaluations are taken bothprior to and subsequent to immersion in alkaline media maintained at apH on the order of those characterizing the alkaline solutions employedin the post-exposure treatment of photographic film. In each case, themelting point evaluations are conducted three days after coating thegelatin solution onto a film base by placing the respective samples inwater and gradually raising the water temperature to a point at whichthe gelatin coating melted, disintegrated or separated from the filmbase. In each case, the gelatin is coated onto the film base at neutralpH, i.e., pH 7. The melting point corresponds to that temperature atwhich the foregoing occurred. The results obtained are tabulated asfollows:

As will be made readily manifest from an inspection of the abovesummarized data, the hardening agents described herein make possible theobtention of a marked increase in melting point of the gelatin coatingcomposition, such delayed hardening effects becoming evident as a resultof exposure to alkaline media. As will be further noted, the hardeningefiects imparted by such compounds are negligible if not non-existentdespite the fact that the gelatin coating containing same was left tostand for a period of three days prior to melting point evaluation. Thedelayed-action property previously discussed is thus very much inevidence. It will also be appreciated that the increase in melting pointobtained extends considerably the adaptability of photographic filmelements containing the instant hardening agents to high speed processmg involving the use of high temperature solutions.

EXAMPLE II This example illustrates the improved hardening eifectsobtainable with the compounds of the present invention when included asa component of a photographic silver halide emulsion.

Several one-kilogram samples of a fine grained chlorobromidephotographic emulsion prepared in conventional manner, each containingapproximately 5% (50 gms./ kilo) of an inert gelatin and havingincorporated therein 20 cc. of a 5% solution of 1,4-butynediol;l,4-dichloro butyne and 3-bromopropene respectively, are coated onto acellulose triacetate film support. A control sample of the identicalemulsion but omitting the hardening agent is likewise prepared. Each ofthe samples is conditioned for 8 days at room temperature and 59%relative humidity prior to melting point evaluation. The melting points,determined in the manner described in Example I, are taken, subsequentto photographic exposure utilizing a Type IB Sensitometer, both beforeand after alkaline development. The results obtained are summarized inTable II below:

As the above data makes manifestly clear, improvement in hardeningproperties similar to that described in Example I is obtained.

As stated hereinbefore, the hardening agents of the present inventiondespite providing improvement in the hardening characteristics of thegelatin coating compositions in no way deleteriously affect thesensitometric properties of the photographic element containing same.Thus, photographic emulsions of the type described in Example II andcontaining varying concentrations of the hardening agents exemplified,following photographic exposure and development exhibited excellentspeed, contrast, density, etc. Moreover, such improvements are realizeddespite the use of highly active photographic processing solutions.Again, the importance of this particular aspect cannot be emphasized toostrongly and especially in view of the fact that efiicacious use of themore conventional hardening agents heretofore provided in the artinvariably requires the conjoint use of one or more additionalingredients for purposes of suppressing, e.g., emulsion fogging.

The hardening agents of the present invention present the furtheradvantage that they are readily adaptable to use in combination with anyof the conventional photographic emulsion addenda, e.g.,speed-increasing agents, anti-foggants, and the like. The inclusion ofmaterials of the latter type is particularly effective in thoseinstances wherein the photographic emulsion product is contemplated foruse under what would ordinarily be considered extreme conditions, i.e.,in terms of solution activity as well as processing temperature.

The improvements described herein are noted to obtain with various typesof gelatin silver halide emulsion, e.g., spectral sensitized emulsions,non-spectral sensitized emulsions, such as, X-ray emulsions and thelike. Furthermore, the light-sensitive silver salt employed may be anyof those described in the art, such as, silver bromide, silver iodide,silver chloride, mixed silver halide, e.g., silver chlorobromide, silverbromoiodide and the like.

The hardening agents of the present invention may likewise be employedin emulsions intended for color photography, e.g., emulsions containingcolor-forming coupling compounds or alternatively, emulsionscontemplated for color development by treatment with a developersolution containing the coupler. Such hardening agents may also be usedwith emulsions intended for use in diffusion transfer processing, colortransfer processing, i.e., processes dependent upon the diffusion ofsilver halide, developer, dye developer, coupler, or dye from thelightsensitive element to a suitable receiving layer.

This invention has been described with respect to certain preferredembodiments and there will become obvious to persons skilled in the artother variations, modifications, and equivalents which are to beunderstood as coming within the scope of the present invention.

What is claimed is:

1. A composition comprising gelatin containing therein at least onehardening compound selected from the group consisting of those of thefollowing structural formulae:

and

(II) CHFCH-CH -Y wherein X is selected from the group consisting ofhydroxy and halogen and Y represents halogen.

2. A composition according to claim 1, further containing alight-sensitive silver halide.

3. A composition according to claim 1, wherein said hardening compoundcomprises 1,4-butynediol.

4. A composition according to claim 1, wherein said hardening compoundcomprises 1,4-dichlorobutyne.

5. A composition according to claim 1, wherein said hardening compoundcomprises 3-bromopropene.

6. A photosensitive element comprising a support coated with thecomposition of claim 2.

References Cited UNITED STATES PATENTS 3,212,900 10/1965 Oguchi et a1.96-109 GEORGE F. LESMES, Primary Examiner R. E. MARTIN, Assist-antExaminer US. Cl. X.R. 96-407;106125;260117 2 3 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,505 ,071 Dated April 71970 Inventor s) SALVATORE EMMI It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

In Table 1, column 4, lines 30-40, the heading over the third column ofdata should read pH 11 instead of "pH 17."

SIGNED AND SEALED AUG4-I970 QSEAL) Attest:

IIMIAII E. SW .18. Edward M. Fletcher, In. Gomissioner o1 Pat ntsAttesting Officer

